Most commercial aircraft are equipped with a Flight Management System (FMS). In most instances, the FMS is implemented with one or more Flight Management Computers (FMCs) or Flight Management Computers Functions (FMFs). These redundant FMSs proceed during normal coupled flight by sequencing through a flight plan that comprises a series of lateral legs that interconnect a plurality of waypoints. In the FMS, as each leg of a flight plan is “sequenced,” the FMS issues guidance commands to the auto-flight system, which controls the aircraft to fly to a new leg and its associated trajectory. The control and signal of a leg sequence between multiple computers during real-time operation is an important system behavior that relies heavily on an additional level of integrity for higher precision aircraft path control during required navigation performance (RNP) operations.
Commercial aviation regulatory agencies have developed required navigation performance (RNP) protocols to facilitate the management of air traffic. Required navigation performance equipped aircraft can safely operate along various routes with less separation than previously needed. This can be significant, because less separation means that the number of aircraft that can safely use a particular airspace may increase, and therefore accommodate the increasing demand for air traffic capacity. Under these protocols, RNP values may be assigned to various segments, or legs, of an aircraft's flight plan. The RNP value defines an airspace within which the aircraft should remain for a predetermined percentage (e.g., 95 percent) of the total flying time, and may be referred to as the RNP corridor. Presently, it is very difficult to provide FMS guidance for procedures with RNP restrictions of ≦0.3 NM, without first requiring a flight crew to undergo significant training to perform the guidance monitoring for each procedure below RNP 0.3.
A traditional redundant FMS has a single queue of events which is stored and managed by one of the FMCs. A leg sequencing event is actually generated by a master FMC (coupled to the auto-pilot) and is imposed on other FMCs. The actual detection of condition to sequence and process the next leg of a flight plan is ultimately acted upon based on only one real-time solution. Thus, while highly unlikely, it is postulated that an error in the master FMC could (and likely would) be propagated to the FMCs. Such a postulated event is incompatible with RNP operations. Independent detection and control of leg sequencing operations would provide the additional level of integrity that can be used to more closely control the flight of an aircraft and provide compatibility with RNP operations.
Hence, there is a need for a flight management system that enables guidance for procedures with RNP restrictions of ≦0.3 NM, thereby alleviating the need for flight crews to undergo significant training. There is also a need for a flight management system that implements a system and method for independently detecting and controlling leg sequencing operations among a plurality of FMCs, to thereby provide fault tolerant lateral waypoint sequencing, and compatibility with RNP operations. The present invention addresses at least this need.